Sulfur-rich corrosion-resistant copper-zinc alloy

ABSTRACT

Copper-zinc alloys exhibiting enhanced oxidation resistance are provided by adding an amount of sulfur that is effective to enhance oxidative resistance. Such sulfur addition can be achieved by forming a sulfur-rich pre-mix that is added to a base alloy composition. This technique provides improved homogeneity and distribution of the sulfur predominantly in the form of a metal sulfide.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. §119(e) to U.S.Provisional Patent Application No. 61/556,376, filed Nov. 7, 2011,entitled “SULFUR-RICH CORROSION-RESISTANT COPPER-ZINC ALLOY”, which isherein incorporated by reference in its entirety.

FIELD

Disclosed are sulfur-rich, corrosion-resistant copper-zinc alloys andmethods for preparing same.

BACKGROUND

Sulfur is typically an incidental impurity in brass alloys, and istypically present in an amount that does not exceed 0.005% by weight. Infact, it is disclosed in the published literature that sulfur in anamount greater than 0.01% by weight may negatively impact brass alloys,causing the brass alloy to become brittle.

However, it is known to add sulfur to brass alloys to impart improvedmachinability. More specifically, sulfur has been added to moltenferrous and non-ferrous alloys (including copper alloys) to promotefree-machining characteristics. The sulfur acts singularly or incombination with other alloy constituents to produce particles that actas chip breakers during machining. For example, U.S. Pat. No. 5,137,685discloses the addition of sulfur to copper alloys, in combination withbismuth, in order to improve machinability. However, this patentexpressly places an upper limit for sulfur at about 2% by weight, andindicates a preference for an amount of sulfur that is from about 0.1%to about 1.0%.

Generally, the insolubility of free sulfur and of sulfur-richinter-metallic compounds in the alloy matrix is understood to determinethe effectiveness of sulfur addition for improving machinability.

It is believed that the known benefit of adding sulfur to a brass alloyis limited to improved machinability, and that the known brass alloysincorporating sulfur, even those exhibiting improved machinability dueto sulfur addition, do not exhibit enhanced corrosion resistance.

SUMMARY

One embodiment includes a copper-zinc alloy having from about 10% toabout 45% zinc by weight, at least about 50% copper by weight, and anamount of sulfur that is effective to enhance the oxidative resistancethereof.

Another embodiment relates to a process for preparing an oxidationresistant copper-zinc alloy by combining sulfur and a pre-mix metalunder conditions suitable for forming a molten alloy pre-mix, preparinga base alloy, and combining the alloy pre-mix and the base alloy, wherethe pre-mix metal is chosen from the group of copper, zinc, aluminum,lead, bismuth, tin or a combination thereof. The base alloy may compriseprimarily copper, primarily zinc, or a mixture of copper and zinc, andmay also contain other alloying additives.

Another embodiment relates to the use of an oxidation-resistant brassalloy as described herein as a component of a water-conveying conduitsystem for potable water.

DETAILED DESCRIPTION

This disclosure is concerned primarily with the use of sulfur to enhancecorrosion-resistance of copper-zinc alloys.

The copper-zinc alloys described herein are generally referred to asbrass alloys or brasses. The terms “brass alloys” or “brasses” usedherein generally refer to an alloy including copper and zinc wherein theelement in greatest abundance is copper and wherein zinc is present inan amount that is in excess of about 10% by weight.

As used herein, the term “oxidative resistance” (or “oxidationresistant”) refers to resistance to dezincification and stress corrosioncracking, and resistance to corrosion in general, or any combination ofthe foregoing.

The expression “substantially free of lead” is generally synonymous withthe expression “lead-free” and refers to a brass alloy that does notcontain any deliberately added lead and only contains very low levels ofunavoidable lead impurities. Such brass alloys that are substantiallyfree of lead contain lead in an amount of about 0.25% or less on aweight basis, such as less than or about 0.2% or less than or about0.1%.

Dezincification is characterized by the selective loss of zinc from abrass alloy. Dezincification is generally caused by contact of a brassalloy with corrosive agents or contaminants, which are commonly found inwater or water vapor. Over an extended period of time (e.g., greaterthan about 3 years), contact between conventional brasses and moisturecauses a white, loose zinc oxide surface deposit to form.

Stress corrosion cracking refers to a type of cracking that occurseither with or without dezincification, and causes a loss of mechanicalstrength and may ultimately result in fracture of an alloy due tointernal stresses associated with the composition or processing of thealloy.

All percentages, unless otherwise indicated herein, refer to the amountby weight of the element, irrespective of whether the element is presentin the alloy in its elemental form or in the form of an inter-metalliccomplex.

The oxidation resistance of brass alloys can be improved by the additionof sulfur. Different alloy types generally require different sulfurlevels to gain optimum oxidation resistance. In general, the enhancedoxidation resistance benefits are expected to apply to substantially allbrass alloys containing zinc in an amount that is in excess of about 10%by weight, for example, from about 10% to about 45% by weight, fromabout 12% to about 40% by weight, and from about 15% to about 35% byweight, or from about 35% to about 45% by weight. The addition of sulfuras described herein is effective for enhancing corrosion resistance ofeither leaded brass alloys or lead-free brass alloys.

Surprisingly, the sulfur additive is at least as effective at impartingoxidation resistance as conventional brass corrosion inhibitingadditives such as selenium, tellurium, lead, tin, iron, nickel,aluminum, manganese, bismuth, antimony, phosphorous, arsenic, etc., andcosts significantly less. While sulfur can be employed as an effectiveoxidation resistance additive for brasses containing conventionalcorrosion inhibiting additives, such conventional corrosion inhibitingadditives are not necessary to achieve effective oxidation resistancewhen a sulfur additive is employed. Eliminating or reducing the use ofconventional corrosion inhibiting additives is expected to mitigateundesirable property changes caused by their addition and reduce oreliminate the need for environmentally undesirable or questionableadditives. Thus, the use of a sulfur as an oxidation resistant additiveas disclosed herein offers a potentially low cost and environmentallymore acceptable technique for achieving oxidation resistance in brassalloys.

There are drawbacks to many of the traditional corrosion inhibitors usedwith brass alloys. For example, additions of arsenic and/or antimony inamounts less than about 0.2% inhibit dezincification of certain brassalloys, but require heat treatment in order to be effective and theadditives are generally ineffective at inhibiting stress corrosioncracking. Nickel, tin, and/or aluminum may be added in amounts rangingfrom about 0.25% to about 2% to inhibit dezincification, but the nickel,tin and/or aluminum additives tend to cause the brass alloy to developundesirable property changes. The use of excess traditional corrosioninhibitors may promote initiation of internal stress corrosion fracturesalong grain boundaries of the brass alloy. In contrast, sulfur appearsto present no risk of stress corrosion cracking as demonstrated byexcellent mechanical performance.

Degrading elements such as iron, manganese, calcium, tellurium andcobalt tend to react with conventional dezincification inhibitors toreduce their beneficial effect, or to cause a deleterious effect on thealloy when the degrading element is present at a high level. The highreaction potential of zinc and sulfur is expected to limit the negativeinfluence of such degrading elements.

Additionally, there are no previously known inhibitor additives that aregenerally effective for fully protecting brasses containing greater thanabout 35% zinc. For brass alloys containing greater than about 35% zinc,the traditional corrosion inhibitors become sensitized to stresscorrosion cracking. However, as described herein, the sulfur additiveprovides increased oxidation resistance for brass alloys with zincconcentrations from about 35% to about 45%. Brass alloys having a zinccontent in excess of about 35% by weight have two separate structuralcomponents, including one that is copper-rich, and another that iszinc-rich. As the zinc content increases the percent of the zinc-richcomponent increases. Corrosion potential increases with a greaterzinc-rich component percentage and the zinc-rich component ispreferentially attacked during both dezincification and stress corrosioncracking, with a dramatic spike occurring above about 38% zinc byweight. Machinability also increases with an elevated percentage of thezinc-rich component, with a dramatic improvement in machinabilityoccurring for a zinc content over 38% by weight.

When sulfur is present in high concentrations in a brass alloy throughlate addition of sulfur to the melt or without employing methods to aidin its distribution throughout the alloy, the sulfur tends to have anuneven distribution in the brass alloy. The uneven distribution of thesulfur, usually in the form of zinc sulfide, negatively impactsmechanical properties of parts made from the alloy. However, thereaction between zinc and sulfur to form a zinc sulfide, which generallyfloats on top of the molten alloy and is removed as slag duringprocessing, generally works to limit sulfur below 0.1% by weight inbrass alloys unless additional methods are used to aid the distributionof the sulfur. The level of sulfur is therefore self-regulated to lowerconcentrations that do not negatively impact mechanical properties dueto the removal of zinc sulfide as slag during processing, and the sulfurwhich remains is generally retained along grain boundaries.

Non-limiting examples of methods to aid in the distribution of sulfurinclude the addition of alloying elements which aid in the distributionof sulfur, including without limitation aluminum and tin, the additionof the sulfur as part of a pre-mix, and the use of certain castingmethods, including without limitation rapid casting solidificationthrough a process such as permanent mold casting. Higher levels ofsulfur in the alloy with a more uniform distribution throughout thealloy may be achieved using such methods.

Sulfur increases oxidation resistance of brass alloys due to an inherentsegregation of zinc sulfide or copper sulfide along alloy grainboundaries. This grain boundary oxidation resistance barrier is similarto that afforded by the addition of the traditional corrosion inhibitingagent arsenic, however, the sulfur-induced oxidation resistance barrierdoes not require heat treatment to develop its oxidation resistance.

The base oxidation resistance that is imparted to a brass alloy bysulfur-enrichment can be increased by grain refinement throughmanufacturing processes. For example, forging and cold-working processesreduce microstructural grain size, limiting pathways for corrosion oroxidation to penetrate into the brass alloy. The permanent mold castingprocess has a similar end result of grain refinement and increasedoxidation resistance because of the rapid solidification of metal duringcasting. The sulfur-enhanced oxidation resistance of castings can alsobe further improved through the addition of traditional grain refiners,such as phosphorus.

Sulfur-enriched brass alloys demonstrate excellent mechanicalproperties, including high ductility, and are considered to be highlyresistant to stress corrosion cracking Also, the observed high ductilityis considered to have an important benefit with respect to cold workingof certain brass alloys. The presence of inter-granular zinc sulfide isbelieved to promote slip along grain boundaries, resulting in reducedyield strength and higher percent elongation for certain brass alloys.

Additionally, aluminum has been found to be effective in retainingsulfur in brass alloys. During alloy melting, it has been observed thatthe retention of sulfur within certain brasses is strongly influenced bya high zinc content in the alloy. The strong affinity of sulfur for zincpromotes the formation of zinc sulfides that tend to float up in thefurnace melt and are ultimately removed from the surface of the bath asslag. Although a portion of the zinc sulfides do remain within the alloyalong grain boundaries in amounts adequate to aid dezincificationresistance, the retention of the sulfur is less predictable. Theaddition of aluminum has been shown to maintain sulfur in the alloy,increasing sulfur recoveries and the consistency of sulfur-enrichment. Asuitable amount of sulfur additive that may be used to achieve enhancedoxidative resistance can be in excess of about 2% by weight, such asfrom about 2.1% to about 4% by weight, or from about 2.5% to about 4% byweight. However, smaller amounts may also be employed to achieve abeneficial improvement in oxidative resistance. When distributedthroughout the brass alloy as described herein, sulfur in amounts as lowas 0.006% are expected to provide some enhancements to the oxidationresistance of the resulting brass alloy.

In addition to the specified amounts of zinc, copper and sulfur, and anyoptional alloying elements previously described, the brass alloysdisclosed herein may contain minor amounts of elements including withoutlimitation silicon, selenium, tellurium, manganese, bismuth, antimony,phosphorous, lead, tin, iron, nickel, aluminum and/or arsenic. Theseelements may be present in amounts from about 0.006% to about 6% byweight, and preferably in amounts from about 0.1% and about 6%, or, fortin and aluminum from about 0.02% to about 6%. These elements may alsobe present in trace amounts in certain embodiments, and lesser amountsmay provide some minor additional benefit for processing. Additionaltrace elements or impurities may also be present in the brass alloys.

Unlike with previously known sulfur additions to brasses, whichgenerally sought to segregate sulfur in larger sulfur-rich phases toimprove machinability, certain processes disclosed herein seek toachieve a more homogeneous distribution of sulfur in the form of muchsmaller particles. In addition, in accordance with certain embodiments,the added sulfur is homogeneously distributed throughout the alloy inthe form of a metal sulfide. The zinc sulfide is fluorescent and showsas a distinct yellow throughout an alloy that has uniform distributionof the sulfide.

The copper-zinc alloys disclosed herein can be prepared by aconventional process in which elemental sulfur is simply added directlyto a brass furnace melt. This method appears to provide less controlover sulfur content than other processes disclosed herein. Additionally,much of the added sulfur tends to float on top of the melt and is notincorporated into the alloy, as described above. Late additions ofelemental sulfur also tend to generate excess sulfur dioxide fuming innon-controlled atmospheres, and may result in substantial sulfur lossdue to the low vapor point of sulfur and the reaction between sulfur andzinc. The risk of release of toxic sulfur dioxide and zinc sulfidereleases can be mitigated through the use of proper melting equipmentand practices, such as the traditional practice of using an inert gascover over the molten bath, which eliminates exposure of the metal tooxygen and mitigates sulfur dioxide evolution.

An alternative method involves combining sulfur and zinc underconditions sufficient to form a molten alloy pre-mix. In this process,elemental zinc and sulfur (e.g., in the form of a powder) are placed ina containment vessel. Oxygen is replaced with nitrogen for some batches,but either atmosphere works satisfactorily to create a sulfur-zincpre-mix. In order to combine the sulfur and zinc, the vessel is heatedto approximately 1000° F. After the vessel has been heated long enoughto combine the elements into a mixture, the vessel is cooled, and thesulfur-rich atmosphere is evacuated. The sulfur-zinc mixture is thenremoved.

A base charge of the copper alloy is prepared in a melting furnace. Thebase alloy includes all additions needed to complete alloying other thanzinc and sulfur. Some elemental zinc can then be added to the base alloycontainment vessel to reduce the melting point of the base alloy whenthe sulfur-zinc mixture is added. The resulting alloy can be cast intoarticles, such as pipe fittings or other components, or cast intoingots. If desired, the solidified brass alloy may be subjected tovarious treatments before being used to fabricate articles. Suchtreatments include without limitation cold-working, annealing, etc.

In another alternative method, sulfur and copper are combined underconditions to form a molten alloy pre-mix. In this process, elementalcopper and sulfur (e.g., powder form) are placed in a containment vesseland heated to a molten state to produce a sulfur-copper pre-mix.Additional elements such as aluminum may be added to the copper-sulfurpre-mix to help retain the sulfur within the pre-mix melt.

In this processing method, a base alloy containing zinc and optionallycontaining copper and/or other elements in minor amounts is prepared.Thereafter, the copper-sulfur pre-mix and the base alloy are combined.Optionally, added zinc, copper and/or other elements may be combinedwith the alloy pre-mix and/or the base alloy. The resulting alloy may becast or treated as stated previously.

Alternatively, after preparation of a copper-sulfur pre-mix, zinc can beadded in a controlled manner to the copper-sulfur pre-mix. The reactionbetween zinc and sulfur is moderated by the foundational sulfur-enrichedcopper-sulfur premix.

It is believed that the processes involving combining sulfur and zinc toform a pre-mix that is combined with a base copper alloy and/or theprocess for combining sulfur and copper to form a pre-mix that iscombined with a base alloy have the effect of ensuring that a largerproportion of the elemental sulfur addition is homogenously distributedwithin the completed alloy, and is present in the form of a metalsulfide (e.g., zinc sulfide or copper sulfide) in higher proportion thanhas been achieved with known techniques of incorporating sulfur within abrass alloy. For example, it is expected that copper zinc alloysprepared in accordance with certain processes disclosed herein willprovide homogenous distribution of sulfur throughout the solid alloypredominately in the form of an intermetallic sulfide (e.g., coppersulfide and/or zinc sulfide).

Once the sulfur alloy has been properly constructed, sulfur levels haveonly modest loss through repeated re-melting. The metal off-fall streamsof manufacturing (such as gating and scrap) can be melted repeatedly forreuse without any significant loss of sulfur.

Another alloy preparation method includes combining sulfur and asecondary alloying ingredient together to create an additive pre-mix.For example, sulfur powders can be melted together with metal powders ormetal solid forms in an oxygen-free containment vessel to producesulfur-metal mixtures that can be added to a molten alloy bathcontaining the remaining constituents of the brass alloy. Certainpre-mix combinations are preferred due to the reaction and loss ofsulfur in specific alloys. The metals that can be used in the premixinclude without limitation, copper, zinc, aluminum, lead, bismuth andtin.

A pre-mix as described herein can also be used to adjust the sulfurcontent in a brass alloy directly before casting.

The addition of sulfur in the form of a copper-based pre-mix may alsoaid in removing oxides from the molten metal. This late alloy additionmay offer an alternative to traditional deoxidizing additives such asphosphorus copper.

In addition to enhanced corrosion resistance, other benefits have beendemonstrated by the disclosed sulfur additions to copper-zinc alloys.For example, heat treatment of such alloys has proven to improvefree-machining properties of sulfur-rich alloys by agglomerating sulfurinto chip-breaking constituents. Corrosion resistance appears to bemodestly degraded by heat treatment and the resultant agglomeration ofsulfur. The amount of sulfur added can be increased in these heattreated alloys to off-set the agglomerated sulfur.

In leaded alloys, it is expected that heat treatment will potentiallysegregate sulfur along with free pockets of lead. In other words, thelead is not expected to significantly go into solution within the alloymatrix, but is instead expected to form discrete volumes of leadagglomerates that improve machinability. Heat treatment (and theresultant segregation of sulfur) is expected to aid machining as asecondary benefit of these alloys.

Additionally, the sulfur additive is expected to reduce the amount oflead leeching from a lead-containing part into potable water. Morespecifically, it is expected that the combination of lead and sulfurwithin the alloy will be less susceptible to leeching.

Preliminary data suggests that the disclosed sulfur treatment does nothave a detrimental effect on soldering, but may actually improvesolderability.

The intermetallic sulfide at the surface of a casting made of thedisclosed alloys appears to be cleaned by zinc chloride flux withoutadverse corrosion or unwanted flux to metal reaction during soldering.

Sulfur treated parts have maintained corrosion resistance after thetreatment with dilute citric acid and/or ultrasonic cleaning.

The copper-zinc alloys described herein are sufficiently resistant tocorrosion via dezincification and stress corrosion cracking that theyare expected to be suitable for use in the fabrication of a plumbingcomponent or other component used in a water-conveying conduit system(e.g., cooling tower piping). Prior to the current disclosure, it wasbelieved that the copper-zinc alloys had inadequate corrosion resistancefor use in plumbing systems or other water-conveying conduit systems.

EXAMPLE 1

One example of the making of brass alloy parts includes melting copper,and adding zinc and aluminum to the melted copper to create a base metalbath. Sulfur is then added directly to the molten metal bath under aninert gas blanket. In this example, the target amount of sulfur added tothe bath was 0.1% sulfur. The inert gas allows retention of some of thesulfur in the bath, though some is lost as a zinc sulfide or because itis otherwise not incorporated into the bath. The molten metal is thenformed into ingots with the following composition: 63.12% copper, about36.76% zinc, about 0.064% aluminum; 0.003% lead and 0.031% sulfur. Thesebase ingots were then melted, and some parts were made by casting andsome by forging. The cast and forged parts each had a composition of:63.46% copper, 37.13% zinc, 0.039% aluminum, 0.001% tin, 0.002% lead,and 0.025% sulfur.

The final chemistry of the part indicates that there is some loss ofadded aluminum, presumably through the formation of aluminum oxide. Somezinc sulfide is also believed to be lost as slag from the mixture.Mechanical properties of the final brass alloy parts according toExample 1 are as shown in Table 1 below. Parts manufactured from thefinal brass alloy exhibited good oxidative resistance when cast, andexceptional oxidative resistance when forged, as shown in Table 2 below.This example demonstrates that there is a corrosion resistance advantageprovided by adding sulfur to a brass alloy even without forging, duelargely to grain boundary corrosion protection. The alloy is furthermade very corrosion-resistant by forging, i.e., refinement of grain. Thecorrosion resistant sulfur alloy could also have been made moreresistant by adding a grain-refiner, including without limitationphosphorous, or by using a process that produced grain refinement due torapid casting solidification, including without limitation permanentmold casting.

EXAMPLE 2

Another example of a brass alloy includes melting of the base alloyingot described above, with a foundation of copper and additions ofzinc, aluminum and sulfur. The base ingot included about 63.12% copper,about 36.76% zinc, about 0.064% aluminum; 0.003% lead and 0.031% sulfur.After the base ingot was melted, tin was added to the molten bath priorto casting. The final brass alloy parts had a chemical composition of63.09% copper, 36.61% zinc, 0.036% aluminum, 0.052% tin, 0.028% lead and0.025% sulfur. The brass alloy was cast using green sand casting, whichdoes not result in inherent grain refinement of the alloy due to theslow rate of solidification cooling, which produces a large grain size.Exceptional corrosion resistance was achieved with cast componentshaving the formulation of Example 2. Cast brasses with similar amountsof zinc are normally sensitive to dezincification corrosion due to theirinherent grain structures. The corrosion resistance of Example 2 wasenhanced by the use of an additional corrosion inhibiting component,tin, in addition to the sulfur. The sulfur and tin are believed tocombine to enhance the corrosion resistance of the alloy matrix.Mechanical properties of the final brass alloy parts according toExample 2 are as shown in Table 1 below. Parts manufactured from thefinal brass alloy exhibited exceptional oxidative resistance as shown inTable 2 below.

TABLE 1 Mechanical Properties Cast (Green Sand) UTS YS % Specimen (psi)(psi) Elongation Example 1: High Zinc - Trace Lead - Low Sulfur AlloyTest Bar 1 45,453 11,690 54.95 Test Bar 2 42,842 12,673 50.65 Example 2:High Zinc - Trace Lead - Low Sulfur Alloy (+Tin) Test Bar 1 41,03012,728 46.5  Test Bar 2 43,162 13,028 48.45

TABLE 2 Corrosion Resistance PASS/ Process Maximum Minimum Average FAIL*Example 1 Green Sand 350  50 200 Fail Casting microns microns micronsForging 100  0 <50 Pass microns microns microns Example 2 Green Sand 200120 160 Pass Casting microns microns microns Test Method: * BS EN ISO6509 & Acceptance Criteria BS EN 13828: Penetration 200 micron max.

EXAMPLE 3

Another example brass alloy was constructed by forming a base alloy byadding zinc to copper without any other intentional elemental addition.The molten bath surface was protected from the atmosphere by a granulargraphite cover material. This base alloy contained 65.35% copper,34.583% zinc, <0.001% aluminum, 0.013% tin, 0.021% lead, and <0.003%sulfur. Some parts were cast out of this molten base alloy forcomparison with sulfur-added parts.

A second sulfur-enriched brass alloy was constructed by again addingzinc to the molten copper starter bath with a cover material of granulargraphite. For this second brass alloy, sulfur was added to theestablished furnace bath by plunging a copper envelope containing powdersulfur. The target sulfur content for this second brass alloy was 0.25%,and sufficient sulfur was added to reach this percentage if all of thesulfur remained in the alloy. The final chemistry of this metal heat was70.09% copper, 29.83% zinc, <0.001% aluminum, 0.011% tin, 0.019% lead,and 0.024% sulfur.

Comparison dezincification testing revealed no corrosion protection forthe first example and an improvement in corrosion resistance for thesulfur-enriched brass alloy. This example also provides a demonstrationof a greater melt loss of sulfur with sulfur directly to the molten baththan with a pre-mix or with the use of additional alloying elements.

EXAMPLE 4

A sulfur brass alloy was built using a pre-mix containing tin andsulfur. The sulfur in the pre-mix was a sufficient amount to target 0.1%sulfur when combined with the base alloy. The tin in the pre-mix wassufficient to allow the sulfur to be evenly dispersed throughout thetin, and amounts from about 6 parts to about 10 parts of tin were usedfor each 1 part of sulfur. When the sulfur was dispersed in the tin, thetin-sulfur pre-mix was added to a base alloy. The base alloy wasconstructed by first adding zinc to the copper and then adding aluminumto aid in later sulfur retention. The prescribed pre-mix was then addedto the established melt directly before casting. The resultant chemistrywas 62.61% copper, 37.05% zinc, 0.036% aluminum, 0.117% tin, 0.012% leadand 0.023% sulfur. Parts were then cast from the combined alloy, andtested with good corrosion resistance.

Corrosion test surfaces showed clear dezincification of the non-sulfuradded alloy. This example indicates the uniformity provided by addingsulfur to the alloy melt as part of a pre-mix.

Standardized tests that can be used to establish “enhanced corrosionresistance” are: ISO 6957—Copper Alloys—Ammonia test for stresscorrosion resistance for stress corrosion cracking; and BS EN ISO6509—Corrosion of metals and alloys—Determination of dezincificationresistance of brass for dezincification resistance.

The pass criteria for the stress corrosion cracking test is that nocracks are evident after test exposure. The sulfur enriched alloy doesnot have cracking. The acceptance criterion used for assessingdezincification corrosion penetration is based on BS EN 13828 and is setat 200 micron penetration. Certain embodiments have achieved nocorrosion penetration for the dezincification test.

It is also important to note that the current disclosure includesexemplary embodiments, and is illustrative only. Although only a fewembodiments of the present innovations have been described in detail inthis disclosure, those skilled in the art who review this disclosurewill readily appreciate that many modifications are possible (e.g.,variations in additives, heating times, heating temperatures, dimensionsand structures manufactured from the alloys, etc.) without materiallydeparting from the novel teachings and advantages of the subject matterrecited. Accordingly, all such modifications are intended to be includedwithin the scope of the present innovations. Other substitutions,modifications, changes, and omissions may be made in the composition,design, operating conditions, and arrangement of the desired and otherexemplary embodiments without departing from the spirit of the presentinnovations.

It will be understood that any described processes or steps withindescribed processes may be combined with other disclosed processes orsteps to form structures within the scope of the present invention. Theexemplary structures and processes disclosed herein are for illustrativepurposes and are not to be construed as limiting.

It is also to be understood that variations and modifications can bemade on the aforementioned compositions, structures and methods withoutdeparting from the concepts of the present invention, and further it isto be understood that such concepts are intended to be covered by thefollowing claims unless these claims by their language expressly stateotherwise.

What is claimed is:
 1. A copper-zinc alloy having an elementalcomposition comprising: from about 10% to about 45% zinc by weight; atleast 50% copper by weight; and an amount of sulfur that is effective toenhance oxidative resistance.
 2. An alloy according to claim 1, in whichthe sulfur is present in the form of a sulfide chosen from the groupcomprising zinc-sulfide, copper-sulfide, and a combination thereof. 3.An alloy according to claim 2, in which the sulfide is homogenouslydistributed throughout the alloy.
 4. An alloy according to claim 1, inwhich the element zinc is present in an amount from about 10% to about40% by weight.
 5. An alloy according to claim 1, in which the elementzinc is present in an amount form about 35% to about 45% by weight. 6.An alloy according to claim 1, further comprising one or more additivesselected from the group consisting of silicon, selenium, tellurium,lead, tin, manganese, bismuth, antimony, phosphorous, iron, nickel,aluminum, and arsenic, each of the one or more additives present in anamount of from about 0.006% to about 6% by weight.
 7. An alloy accordingto claim 1, in which the sulfur is present in an amount that is betweenabout 0.006% and about 4% by weight.
 8. An alloy according to claim 1,in which the sulfur is present in an amount of from about 2.1% to about4% by weight.
 9. An alloy according to claim 1, in which the sulfur ispresent in an amount of from about 0.006% to about 2.0% by weight. 10.An alloy according to claim 1, in which the sulfur is present in anamount of from about 0.006% to about 0.10% by weight.
 11. An alloyaccording to claim 1, in which the sulfur is predominantly present inthe form of an intermetallic sulfide.
 12. A water-conveying conduitsystem comprising: a conduit component fabricated from a copper-zincalloy according to claim
 1. 13. A process for preparing an oxidationresistant copper-zinc alloy, comprising: combining sulfur and a pre-mixmetal under conditions to form a molten alloy pre-mix, wherein thepre-mix metal is chosen from the group consisting of copper, zinc,aluminum, lead, bismuth, tin, and a combination thereof; preparing abase alloy; and combining the alloy pre-mix and the base alloy.
 14. Aprocess according to claim 13, wherein the pre-mix metal comprises zinc.15. A process according to claim 13, wherein the pre-mix metal comprisescopper.
 16. A process according to claim 15, wherein the pre-mix metalfurther comprises aluminum.
 17. A process according to claim 16, whereinthe pre-mix metal further comprises tin and lead.
 18. A processaccording to claim 13, wherein the base alloy comprises copper.
 19. Aprocess according to claim 13, wherein the base alloy comprises zinc.20. A process according to claim 19, wherein the base alloy furthercomprises copper.
 21. A process according to claim 13, in which theresulting alloy is solidified and subsequently heat treated to enhancemachinability.